1. Field of the Invention
This invention relates to an ink jet recording apparatus of the continuous jet type and a method of automatically adjusting an ink jet jetting axis (nozzle axis) of a continuous jet type ink jet recording apparatus, and more particularly to a continuous jet type ink jet recording apparatus wherein a jet of ink jetted from a nozzle is selectively charged and deflected to record an image on a record medium and an automatic ink jet jetting axis adjusting method of the same.
2. Description of the Prior Art
Various ink jet recording apparatus of the continuous jet type are conventionally known and practically used. An exemplary one of such conventional continuous jet type ink jet recording apparatus is disclosed, for example, in U.S. Pat. No. 3,916,421 and shown in FIG. 4. Referring to FIG. 4, the continuous jet type ink jet recording apparatus shown is formed as an ink jet recording apparatus of the rotary drum type and includes, as principal components thereof, a nozzle 1 into which pressurized ink is supplied, an ink electrode 2 for holding the potential of ink in the nozzle 1 at the ground level, a controlling electrode 3 having a circular opening or a slit-like opening coaxial with the nozzle 1 and connected to receive a controlling signal Sc to control charging of a jet of ink, a grounding electrode 4 disposed in front of the controlling electrode 3 and grounded itself, a knife edge 5 mounted on the grounding electrode 4, a deflecting high voltage dc power source (hereinafter referred to as deflecting power source) 6, a deflecting electrode 7 connected to the deflecting power source 6 for cooperating with the grounding electrode 4 to produce therebetween an intense electric field perpendicular to an ink jet flying axis to deflect a charged ink drop to the grounding electrode 4 side, a recording signal generator SG connected to a host computer or a like signal source not shown for generating a recording signal, and a high voltage switch HVS for amplifying the voltage of the recording signal from the recording signal generator SG to produce a controlling signal Sc necessary for control of charging of an ink jet. An ink drop charged by the controlling electrode 3 is flown to a record medium RM wrapped around a rotary drum DR.
In such conventional continuous jet type ink jet recording apparatus, when a positive voltage is applied to the controlling electrode 3, an ink jet is charged with the negative charge and is disintegrated into a train of ink drops. When the ink drops charged with the negative charge pass a deflecting electric field generated by and between the controlling electrode 3 and the grounding electrode 4, they are reflected to the grounding electrode 4 side by the deflecting electrode 4 so that they are thereafter intercepted by the knife edge 5. On the other hand, when the voltage to the controlling electrode 3 is 0 volt, the ink jet is disintegrated into a train of ink drops while it is not charged, and consequently, the ink drops thereafter advance straightforwardly without being influenced by the deflecting electrode 7 so that the pass by the knife edge 5 and are recorded onto the record medium RM wrapped around the rotary drum DR.
Accordingly, it is apparent that the positional relationship between the ink jet jetting axis and the knife edge 5 is an important factor. In particular, the positional relationship must be such that ink drops charged and deflected be intercepted by the knife edge 5 but non-charged and straightforwardly advancing ink drops pass by the knife edge 4. Generally, the amount of deflection of a charged ink drop ranges 0.1 to 0.4 mm or so at the position of the knife edge 5. Accordingly, the positional relationship between the ink jet jetting axis and the knife edge 5 must be adjusted delicately.
Such adjustment of the positional relationship between the ink jet jetting axis (nozzle axis) and the knife edge is disclosed, for example, in Japanese Patent Laid-Open Application No. 1322/1990. The document discloses a continuous jet type ink jet recording apparatus wherein an ink jet jetting axis (nozzle axis) and a gutter member (corresponding to the knife edge 5) are movable relative to each other and adjustment of the positional relationship between them is performed by manual operation. When the relative position between an ink jet and the gutter member is to be adjusted, the substantial amount of deflection of the ink jet by the deflecting electric field is reduced (for example, to one half) comparing with that upon normal recording. Further, a charge amount detector is connected to the gutter member and the output of the charge amount detector is monitored so that it can be discriminated readily whether or not ink drops come to the gutter member.
In the conventional continuous jet type in jet recording apparatus, when the positional relationship between the ink jet and the gutter member is to be set and adjusted, the substantial amount of deflection of the ink jet by the deflecting electric field is reduced from that when normal recording is performed as described above. However, since the number of parameters of deflection upon adjustment is only one, there are drawbacks that it cannot be confirmed by what degree of accuracy the amount of deflection has been adjusted, that precise adjustment cannot be achieved unless the mechanical accuracy is high, that, if a high degree of mechanical accuracy is achieved, then the production cost of the product will increase as such, and so forth. Especially, while the gutter member must have an insulating structure when a charge amount detector is connected to the gutter member, since the gutter member is always exposed to ink, there is a problem that much difficulty and complication in structure are involved in such insulating structure.
Taking the foregoing into consideration, the inventor of the present invention has proposed, in Japanese Patent Laid-Open Application No. 151251/1992, a continuous jet type ink jet recording apparatus wherein, while a rotary drum and a carriage are held stopped with the carriage positioned in a region within which normal recording is not performed (such position of the carriage will be hereinafter referred to as home position), the continuous jet type ink jet recording apparatus is rendered operative to perform test printing in which an ink jet is jetted and deflected a little with respect to a middle point between two paths along which the ink jet follows when the deflecting electric field is operative and inoperative and the charge (electric current) carried by the ink jet having passed by the knife edge is detected to detect the position of the ink jet jetting axis (nozzle axis).
Another continuous jet type ink jet recording apparatus has also been proposed by the inventor of the present patent application and is disclosed in applicant's co-pending U.S. patent application Ser. No. 07/784,719 filed Oct. 30, 1991 and in applicant's Japanese Patent Laid-Open Application No. 173151/1992 wherein the continuous jet type ink jet recording apparatus is rendered operative to perform test printing wherein an ink jet is jetted and is subject to deflection which varies continuously or stepwise and the charge (electric current) carried by the ink jet having passed by the knife edge is detected to detect the position of an ink jet jetting axis (nozzle axis).